A Method of Manufacturing Footwear and Footwear Manufactured by Direct Injection Production

The invention relates to a method of manufacturing footwear by a direct injection production (DIP).

Further, the invention relates to footwear manufactured by direct injection production (DIP).

It is known in the art to manufacture footwear by means of direct injection of the sole to the upper, whereby injected material serves as a sole or part of a sole, when cured, and serves to attach the footwear upper to the sole construction.

The direct injection process (DIP) or direct injection production (DIP) as it also may be referred to in the following, is advantageous in many ways as the manufactured footwear may be produced to possess both flexibility and strength at the same time.

Various methods have been utilized in the prior art to improve the direct injection process as well as footwear produced by such methods, e.g. in order to increase production efficiency, lower costs, increase comfort to the user, etc.

US 2004/0143995 A1 discloses a direct attach footwear construction, wherein a boot is constructed with an outsole that is direct attached to a midsole which is direct attached to an upper. The outsole is manufactured from a relatively hard rubber or other sufficiently and wear-resistant material and is manufactured, e.g. injection moulded, in advance prior to the direct attachment of the outsole to the footwear.

As an example of a further footwear construction, foam articles that may serve as a cushioning element for an article of footwear, wherein the cushioning element may be a midsole, is disclosed in WO 2021/183475 A1. The cushioning element may be foamed by use of a foaming agent such as a super critical fluid comprising a supercritical nitrogen or a supercritical carbon dioxide. However, this requires further production steps, thereby increasing costs, as the midsole as disclosed by this document is joined to the footwear upper by an adhesive and the midsole is further joined to an outsole by an adhesive.

Thus, it is apparent that such cushioning elements are not suitable for direct injection production of footwear, wherein a sole construction is attached to a footwear upper by direct injection process.

It has been realized that improvements of the method of manufacturing footwear by a direct injection process as well as improvements of footwear manufactured by such a direct injection process are desirable to reduce costs and to improve user comfort as well.

In a first aspect, the invention relates to a method of manufacturing footwear by a direct injection production (DIP), said method comprising

Hereby a footwear may be manufactured by a direct injection production (DIP), wherein a sole part that has been manufactured by a supercritical foaming process and thus comprises desirous characteristics, may readily be applied as part of the sole structure. Such desirous characteristics of a sole part that has been manufactured by a supercritical foaming process may be for example a softer sole that weighs less than a sole part that is made for example of foamed PU (Polyurethane), e.g. PU that is injected in the DIP process and expanded/cured in the DIP mould. Furthermore, less energy may be used in the manufacturing process when using a sole part manufactured by a supercritical foaming process in a DIP process.

Thus, by the invention it is achieved that a direct injection production process (DIP) can be applied for footwear constructions, wherein a sole part that has been manufactured by a supercritical foaming process is comprised and whereby separate joining processes may be avoided.

According to an embodiment, said attaching sole part that serves for attaching said footwear upper to said at least one premanufactured sole part, may serve as at least part of a further sole part of the sole structure of said footwear.

Thus, it will be understood that the attaching sole part may be constituted by a relatively thin layer of injected material that expands and cures. Also, it will be understood that such a relatively thin layer of injected material may not have a homogenous thickness but may comprise one or more areas having an increased thickness, e.g. in view of the configuration of the respective surfaces of the e.g. bottom surface of the footwear upper and the premanufactured sole part and in view of the mutual positioning of the bottom surface of the footwear upper and the premanufactured sole part. Thus, a footwear may be manufactured by a direct injection production (DIP), wherein the attaching sole part may further serve as a sole part in itself, e.g. as a midsole, part of a midsole, an additional midsole or other sole parts that e.g. may attach the footwear upper to a lower placed part of the sole structure such as an outsole or a midsole.

According to an embodiment, said at least one premanufactured sole part may be configured to form an outsole.

Hereby it may be achieved that a footwear may be manufactured by a direct injection production (DIP), wherein the outsole is provided as a premanufactured part that has increased softness and being in lightweight form, i.e. with low density, thus meaning that the outsole may have a desired thickness without adversely affecting the weight of the finished footwear. Thus, it is possible to manufacture footwear by a DIP process having outsoles which have increased thicknesses as compared to hitherto DIP manufactured footwear wherein outsoles made of e.g. PU have been used, and still having a lighter total weight as compared to the traditionally manufactured footwear.

According to an embodiment, said at least one premanufactured sole part may be configured to form a midsole.

Hereby it may be achieved that a footwear may be manufactured by a direct injection production (DIP), wherein a midsole is provided as a premanufactured part that has increased softness and being in lightweight form, i.e. with low density, thus meaning that the midsole may have a desired thickness without adversely affecting the weight of the finished footwear. Thus, it is possible to manufacture footwear by a DIP process having midsoles which have increased thicknesses as compared to hitherto DIP manufactured footwear wherein midsoles made of e.g. PU have been used, and still having a lighter total weight as compared to the traditionally manufactured footwear.

It is noted that in such a case, an outsole may have been attached to the premanufactured midsole by e.g. adhesive or in any other suitable manner in advance.

According to an embodiment, said attaching sole part that is at least partly provided by said injection material upon curing, may form at least part of a midsole.

Hereby it may be achieved that a footwear may be manufactured by a direct injection production (DIP), wherein the at least one premanufactured and super critically foamed sole part may be attached directly by the midsole, i.e. by the injection material, to the upper of the footwear or to another part of the footwear.

Thus, the advantages of the DIP manufacturing process may be used fully.

According to an embodiment, said at least one premanufactured sole part may be premanufactured by subjecting a basic part to a supercritical foaming agent, whereby the basic part is expanded into a preform.

Hereby, a basic part that has been manufactured using e.g. granular thermoplastic materials that have been injected into an initial “baby size” form, is subjected to the supercritical foaming agent and expanded into a preform, which as regards form, size, etc. corresponds to the actual size of the actual footwear, but such that the premanufactured sole part may be positioned into the direct injection mould. During the direct injection process, wherein the heated injection material is injected and thus subjecting heat and pressure to the parts in the mould, the premanufactured sole part will take its final form as regulated by the direct injection mould.

According to an embodiment, said supercritical foaming agent may be a gas such as carbon dioxide (CO2) and/or Nitrogen.

Hereby, the supercritical foaming may be performed in a manner whereby the premanufactured sole part may be manufactured, e.g. foamed, using gasses that are natural ingredients in the atmospheric air and thus do not represent any disadvantages as regards toxic and/or other environmentally undesirous characteristics. Further, such gasses may be recyclable in gas recovery facilities.

According to an embodiment, said at least one premanufactured sole part may comprise TPU (Thermoplastic Polyurethane), TPE (Thermoplastic Elastomer), PEBAX® (Polyether Block Amide), natural rubber, synthetic rubber, ethylene vinyl acetate (EVA) and/or polyvinyl chloride (PVC).

Other materials may be used instead or additionally.

According to an embodiment, said injection material may comprise PU (Polyurethane), latex, polyvinyl chloride (PVC), and/or thermoplastic rubber (TR).

Other materials may be used instead or additionally.

According to an embodiment, said at least one premanufactured sole part may be configured with a ground facing surface and a foot facing surface, wherein said foot facing surface comprises at least one indentation for receiving injection material.

Hereby, it may be achieved that the soft and low-density material of the premanufactured and super critically foamed sole part, e.g. the outsole, may be affected by the harder material of the injection material, e.g. PU that in connection with the injection and/or expansion will enter the at least one indentation. Upon curing, when the injected material of e.g. a midsole has been attached to the e.g. outsole, the cured material in the at least one indentation will have a strengthening effect on the softer material of the e.g. outsole, depending on the size and shape of the at least one indentation.

It is apparent that the indentation may have any shape and size and that as specified at least one indentation may be present, e.g. one, two, three, etc.

According to an embodiment, said at least one indentation for receiving injection material that is comprised in said foot facing surface may form a groove along the foot facing surface.

Hereby, it may be achieved that the soft and low-density material of the premanufactured and super critically foamed sole part, e.g. the outsole, may be affected by the harder material of the injection material, e.g. PU, such that an increased rigidity may be achieved in a direction along the direction of the at least one indentation. Hereby, the e.g. softness and the flexibility of the e.g. outsole may be designed by the lay-out of the at least one indentation/groove and/or by the depth of the at least one indentation/groove.

According to an embodiment, said at least one indentation for receiving injection material that forms a groove along the foot facing surface, may be extending in a longitudinal and/or transversal direction of the footwear.

Hereby, it may be achieved that an increased rigidity may be achieved in a direction along the longitudinal direction of the footwear and/or along a direction transverse to the longitudinal direction of the footwear. Hereby, the e.g. softness and the flexibility of the e.g. outsole may be designed by the lay-out, e.g. direction of the at least one indentation/groove and/or by the depth of the at least one indentation/groove.

According to an embodiment, said at least one indentation for receiving injection material that forms a groove along the foot facing surface, may be extending in a direction that essentially forms an angle different from 0° in relation to the longitudinal direction of the footwear.

Hereby, further options for configuring the footwear to obtain a desired e.g. softness and flexibility of the e.g. outsole may be achieved, e.g. by designing the lay-out, e.g. direction/angle of the at least one indentation/groove and/or by the depth of the at least one indentation/groove.

According to an embodiment, said at least one indentation for receiving injection material that forms a groove along the foot facing surface, may be extending essentially linearly, in angular forms and/or in curved forms.

Hereby, even further options for configuring the footwear to obtain a desired e.g. softness and flexibility of the e.g. outsole may be achieved, e.g. by designing the lay- out, e.g. direction/angle and/or form of the at least one indentation/groove and/or by the depth of the at least one indentation/groove.

According to an embodiment, said at least one indentation for receiving injection material may extend through said at least one premanufactured sole part.

Hereby, even further options for configuring the footwear to obtain a desired e.g. softness and flexibility of the e.g. outsole may be achieved, e.g. by having one or more parts of the injected material reaching through the premanufactured sole part and thus possibly forming part of the ground facing surface of the outsole, thereby influencing also on the characteristics of the ground facing surface of the outsole such as e.g. friction to the ground, rigidity, wear resistance of the outsole, etc.

According to an embodiment, said at least one indentation for receiving injection material may be configured asymmetrically in/on said foot facing surface.

Hereby, the support of the sole, e.g. hardness, the comfort etc. may be adapted to the user, e.g. with the indentation areas, when filled with the relatively hard composition of the cured injection material as compared to the softer SCF foamed material of the premanufactured sole part, may provide load bearing areas, e.g. at the heel and the ball of the foot, while the softer SCF foamed material may provide a larger degree of comfort at other areas. Furthermore, it will be understood that such a “tuning” of hardness/comfort, e.g. to achieve a variable hardness, may be utilized to adapt the footwear in view of specific users, e.g. in order to provide larger support at the medial side or at the lateral side, etc.

According to an embodiment, said at least one indentation for receiving injection material may be configured for providing a variable hardness and/or support of the sole structure.

According to an embodiment, said at least one premanufactured sole part may comprise a bonding layer on at least part of a surface subjected to said injection

Hereby, the adherence to the injection material, once cured and thus the adherence to the attaching sole part may be facilitated, e.g. increased and made stronger.

According to an embodiment, said bonding layer may comprise materials such as glue, textile, woven or non-woven materials, scrim, etc.

According to an embodiment, at least part of said surface subjected to said injection material may be void of said bonding layer, e.g. bottom and/or sides of indentations, etc.